Electric igniting apparatus for internal combustion engines



Dec. 27, 1955 w B SMITS 2,728,807

ELECTRIC IGNIT'ING APPARATUS FOR INTERNAL COMBUSTION ENGINES Filed Dec. 18, 1950 ZZ rE/v ram A473? 5 A175 5M1);

nited States Patent ELECTRIC IGNITING APPARATUS FOR INTERNAL COMBUSTION ENGINES Wytze Beye Smits, Voorburg, Netherlands, assignor to Smitsvonk N. V., Rijswijk, Netherlands Application December 18, 1950, Serial No. 201,307

2 Claims. (Cl. 123148) The invention relates to an electric igniting apparatus for an internal combustion engine, particularly an aeroplane-motor, comprising a generator of current impulses having one or more condensers adapted to be loaded periodically at a voltage of 5000 volts at the most, one or more surface discharge sparking plugs for each cylinder In comparison with the normally used electric igniting apparatus for aeroplanes the igniting apparatus according to the invention has many advantages.

In the usual igniting systems operating at high voltages many difficulties are encountered in connection with the insulation, especially, when the systems are used in the rarefied air at great altitudes. In order to prevent direct discharges between the conducting parts and the neutral mass of the aeroplane the cables leading to the plugs, the plugs themselves and the remaining live parts of the system must be provided with a substantial insulation. In order to avoid the corona-effect the conductors themselves must have relatively great diameters.

Owing to these conditions the parts of the igniting apparatus require much room and have a considerable weight. It has been proposed to meet the difiiculties encountered with the known igniting systems in rarefied air by accommodating all live parts of said systems in metal casings and tubes, in which casings and tubes the pressure is raised. This solution of the problem renders the igniting apparatus still bigger, heavier and more r complicated.

It has also been suggested to generate current impulses of relatively low voltages by means of a low tension generator system and to lead these impulses to transformers built in the sparking plugs themselves, which transformers considerably raise the voltage of the incoming impulses. Also these systems require much space, are complicated and do not prevent that the sparking plugs have to be provided with extra long insulators.

The weight and the dimensions of the mentioned known igniting apparatus may not be underestimated, since particularly aeroplane engines are provided with many cylinders each having often two sparking plugs. The great dimensions of the engines provided with the known igniting systems also render the resistance in the air during flying considerable. Moreover the big parts of the igniting system provided outside the motorblock hamper the natural cooling of the motor. The unprotected high tension cables of the known igniting systems may cause wireless interferences. In order to avoid these interferences special steps have to be taken.

According to the invention all these disadvantages are avoided. Since the entire system operates at low voltage the insulation requires not much attention. The connecting conductors or cables may be made relatively thin. These cables may be enclosed by metal jackets or sleeves, which may be secured directly to the mass of the motor. Wireless interferences caused by the igniting system are thus prevented. All parts of the igniting system may be carried out at a much smaller scale, so that the weight thereof can be considerably decreased. The pressure of the surrounding air has practically no influence on the reliability of the igniting apparatus. The insulators of the sparking plugs and the cables connected thereto are of such small sizes that they cannot seriously hamper the cooling of air cooled motors. The temperature of the cables has no noticeable effect on the reliability of the insulation. This enables the metal-clad cables of being secured directly to the motor block. The cables may even be passed through parts of said casing.

Conductors having a cross section of 0.04" and covered by an insulating layer of about 0.02 and a metal sleeve of which the thickness is also about 0.02, so that the total diameter of the cables is about 0.12, may be used without any difficulty in igniting systems according to the present invention. If a more or less heat-resisting insulating material is used, the cables may be heated above C. before the condition of the insulating becomes dangerous for the relatively low voltages used in the igniting system. The direct attachment of the electric cables to the motor block or casing has also the advantage, that said cables vibrate less. Breakage of the cables by continuous vibration thereof as often occurs in the known high-tension igniting systems is thus avoided.

By using the system according to the invention the dead weight of an aeroplane can be considerably decreased, so that the paying load thereof may be greater.

For the elucidation of the invention reference is made to the accompanying drawing which diagrammatically illustrates a part of an internal combustion motor provided with a surface discharge sparking plug and an electric generator for the operation of said plug.

In the drawing 1 is the block of an internal combustion engine, of which the cylinders 2 and the valve space are covered by a lid 3 carrying a surface discharge sparking plug 4, the construction of which is known per se and need no further description. The central electrode of said plug is fed through an electric conductor 5 which is insulatedly passed through a metal tube 6. This conductor 5 is connected to one fixed contact 7 of a magnetic throw-over switch, of which the other fixed contact 8 is connected to one end of the high-tension winding 9 of a transformer. The other end of said winding 9 is coupled with one end of the low-tension winding 10 or" said transformer and with one end of the coil 11 of the electromagnet for actuating the movable contact 12 of the throw-over switch. The other end of the transformer winding 10 is connected to a battery 13. The other end of coil 11 is coupled with an interruptor 14 which is driven synchronously with the engine. The other side of the interruptor 14 is connected to the battery 13 and to one plate of an igniting condenser 15 of which the other plate is connected to the movable contact 12 of the throw-over switch. Said movable contact is loaded by a spring 16.

The common connection between the condenser 15', the interruptor 14 and the battery 13 is connected to the mass by a second insulated conductor 17 provided in the metal tube 6. Instead of this conductor 17 the mass of the engine or the tube 6 itself may be used as return conductor. In that case the second conductor in the tube 6 may be connected to a second spark plug. In aeroplane motors often two spark plugs per cylinder are used.

If the interrupter has closed its contact the throw-over switch is drawn by the electromagnet in its left hand position, in which position the condenser is connected to the high-tension winding of the transformer. As soon as the interruptor breaks the primary circuit of the transformer a current impulse is generated in the secondary winding of the transformer, by which impulse the condenser is loaded. A very short time after the loading of condenser 15, the movable switch contact is released by the electromagnet and moved into the right hand side by the spring 16. switch the condenser is discharged through the sparking plug. When thereupon the interrupter closes the primary circuit again the switch returns'into its left hand position in order to enable the condenser of being loaded again.

The tube 6 is directly secured to the motorblock by fastening means 18. Since the operating voltage of the igniting apparatus is relatively low (not more than 5000 volts) the insulation of the conductors is rather thin, so that the tube has an over-all diameter of 0.28" at the most.

What I claim is:

1. In an electric ignition system, particularly for an aircraft internal combustion engine, and including a low tension ignition device developing a voltage of 5000 volts, at the most, and a low tension surface discharge spark plug for each cylinder of the engine; a conductor for elec- In this new position of the throw-over trically connecting the ignition device to each of the surface discharge spark plugs, said conductor comprising a metal clad cable having at least one insulated conductor therein and extending adjacent to, and in intimate contact with, the engine block and related cylinder for substantially its entire length, and means for securing said metal clad cable to the engine block and related cylinder in intimate contact with the block and cylinder so that vibration of said cable, due to operation of the engine, is prevented to avoid vibrational fatigue and failure of the conductor.

2. In an electric ignition system; a conductor according to claim 1, wherein said metal clad cable has an outer diameter of less than 0.28 inch to minimize the weight of the ignition system while affording sufiicient insulation to prevent shorting or" the low tension igniting current flowing in said conductor.

References Cited in the file of this patent UNITED STATES PATENTS Smits Aug. 9, 1949 

